1. Field of the Invention
This invention relates to electrophotographic reproduction apparatus and methods for registering sheets and more particularly to apparatus and methods for control of a stepper motor drive for controlling movement of a receiver sheet into transfer relationship with an image-bearing member that supports an image to be transferred to the receiver sheet.
2. Brief Description of Available Systems
In known electrophotographic copier, printers or duplicators the problem of accurate registration of a receiver sheet with a moving member supporting an image for transfer to the sheet is well known. In this regard, reference is made to U.S. Pat. No. 5,322,273, the contents of which are incorporated herein by reference.
Typically, an electrophotographic latent image is formed on the member and this image is toned and then transferred to a receiver sheet directly or transferred to an intermediate image-bearing member and then to the receiver sheet. In moving of the receiver sheet into transfer relationship with the image-bearing member, it is important to adjust the sheet for skew. Once the skew of the sheet is corrected, it is advanced by rollers driven by stepper motors towards the image-bearing member. During the skew control adjustment, the adjustment is implemented by selectively driving the stepper motor driven rollers, which are controlled independently of movement of the image-bearing member. Typically, movement of the receiver sheet and operations performed thereon by various stations are controlled using one or more encoders. Known registration control systems use a transfer roller with which an encoder wheel is associated. This encoder is used for controlling registration of the sheet. For instance, a registration apparatus is disclosed in U.S. Pat. No. 5,731,680, the contents of which are incorporated herein by reference.
However, previous registration apparatus and methods have been limited in that they can only process and register receiver sheets that arrive at the registration mechanism within a narrow operating time window. Sheets that arrive too early or too late can result in erroneous registration or they can cause the registration system to stop and provide an error indication. It is, therefore, an object of the invention to provide improved methods and apparatus for ensuring accurate registration of receiver sheets that arrive in a larger operating time window.
In accordance with one aspect of the invention, there is provided an apparatus for moving a receiver into a registered relationship with a moving image-bearing member. The apparatus includes a motor and a drive member that engages the receiver. A drive coupling is provided to connect the motor to the drive member. The apparatus also includes a sensor that detects a lead edge of the receiver and a timer that determines the delay time between actual detection of the receiver by the sensor and the expected time of detection. Means are provided for controlling the motor to accelerate the movement of the receiver to a speed greater than the image-bearing member speed for a period of time sufficient to account for the amount of delay time, and to decelerate movement of the sheet to a speed substantially equal to the image-bearing member speed.
In accordance with another aspect of the invention, there is provided another apparatus for moving a receiver into a registered relationship with a moving image-bearing member. The apparatus includes a motor and a drive member that engages the receiver. A drive coupling is provided to connect the motor to the drive member. The apparatus also includes a sensor that detects a lead edge of the receiver and a timer that determines the delay time between actual detection of the receiver by the sensor and the expected time of detection. Means are provided to stop the movement of the receiver for a period of time sufficient to maintain a gap between the receiver and a preceding receiver based the time at which the receiver was detected by the sensor, and to accelerate the movement of the receiver to a speed substantially equal to the image-bearing member speed.
In accordance with yet another aspect of the invention, there is provided a method of moving a receiver into a registered relationship with a moving image-bearing member in a registration mechanism. The method includes the step of determining that the receiver arrived at the registration mechanism an amount of delay time later than expected. The movement of the receiver is then accelerated to a speed greater than the image-bearing member speed for a period of time sufficient to account of the amount of delay time. Then the movement of the receiver is decelerated to a speed substantially equal to the image-bearing member speed.
In accordance with a further aspect of the present invention, there is provided a method of moving a receiver into a registered relationship with a moving image-bearing member in a registration mechanism. The method includes the step of determining that the receiver arrived at the registration mechanism an amount of delay time earlier than expected. The receiver is then brought to a stop for a period of time sufficient to account for the amount of time by which the receiver arrived early. Movement of the receiver sheet is then accelerated to a speed substantially equal to the image-bearing member speed.
The invention and its various advantages will become more apparent to those skilled in the art from the ensuing detailed description of preferred embodiments, reference being made to the accompanying drawings.